Prior to this invention it has been the practice to mount a sabre saw cutting blade on a straight blade holder which is reciprocated along a linear path. The sabre saws described in U.S. Letters Pat. Nos. 2,902,067 (issued on Sept. 1, 1959 to R. C. Oakley) and 2,970,484 (issued to W. E. Springer on Feb. 7, 1961) are typical of this construction.
It also has previously been proposed to provide an aggressive cutting action by orbiting the saw blade so that is moves into the end of the kerf during the upward, cutting stroke and away from the end of the kerf on the downward, return stroke. The saws described in U.S. Letters Pat. Nos. 3,457,796 (issued to H. K. Leach et al on July 29, 1969) and 3,374,814 (issued to A. Kaufmann on Mar. 26, 1968) are typical of the foregoing orbital saw blade motion.
The orbital saw blade motion mentioned above is conventionally achieved by pivotally mounting either the saw blade or the blade holder and by rocking the pivotally mounted part as the blade holder is vertically reciprocated. Although such a blade movement provides an advantageous aggressive cutting action, the mechanism for both rocking and reciprocating the saw blade is more expensive as compared with those drive mechanisms that provide only for linear reciprocation of the saw blade.
The present invention achieves a corresponding aggressive cutting action without requiring the saw blade or the saw blade holder to be pivotally mounted and without requiring the mechanism for rocking the pivotally mounted part. This is accomplished by providing the blade holder with an arcuate or curved configuration and by mounting the blade holder so that it reciprocates along a curved path that is determined by its curved configuration. The curvature is such that the saw blade is provided with a rectilinear component of motion which is in the direction of feeding (i.e., the direction in which the saw blade teeth are urged against the workpiece) on the upward cutting stroke and which is in the opposite direction or away from the end of the kerf on the downward cutting stroke. As a result, the teeth on the saw blade are moved into the end of the kerf with an aggressive cutting action on the upward, cutting stroke and away from the end of the kerf on the downward, return stroke.
In the preferred embodiment of this invention the blade holder has a uniform radius of curvature and is bowed in the direction of feeding towards the end of the kerf.
With the foregoing in mind, a major object of this invention is to provide a novel sabre saw in which an aggressive cutting action is achieved by providing the blade holder with an arcuate configuration and by mounting the holder so that is reciprocates along its axis of curvature.
It heretofore has been the practice to secure the sabre saw blade to the blade holder by means of a screw which extends through a screw hole in the saw blade shank and which is threaded into the holder to confine the saw blade shank between the screw head and an opposing face on the holder. This technique of mounting the saw blade was found to unsatisfactory when the blade holder is formed from powdered metal because stress concentrations around the screw hole subject the powdered metal holder to structural failure especially during such cutting operations as plunge cutting.
The present invention overcomes the foregoing problem by providing a novel chuck or blade mounting assembly which distributes the stresses developed during operation to avoid structural failure of powdered metal blade holders. According to a preferred embodiment of this invention, the saw blade mounting assembly comprises a channel shaped reinforcing member which receives the lower end of the blade holder and which is secured to the blade holder by a nut and screw assembly. The screw extends through the reinforcing member with a relatively tight fit. However, the screw hole through the blade holder is oversized to provide a loose fit between the holder and the screw. As a result, all of the forces transmitted by the saw blade to the screw are applied to the reinforcing member rather than directly through the screw to the blade holder. The forces applied to the reinforcing member are applied to the blade holder through stress distributing ear portions on the reinforcing member.
Thus, a further object of this invention is to provide for a novel sabre saw blade mounting assembly that distributes the stresses developed during sawing and thereby reduces the likelihood of structural failure of the blade holder.
As shown in the previously mentioned Springer Pat. No. 2,970,484, a blade holder drive gear is drive connected by one scotch yoke mechanism to the blade holder and by another scotch yoke mechanism to a counterweight which reciprocates to counterbalance the effect of the reciprocating blade holder and saw blade assembly. As compared with the axial length of the drive gear and counterweight assembly in this patent, the present invention provides for a corresponding assembly of greater axial compactness.
Thus, another important object of this invention is to provide a novel sabre saw having an axial compact arrangement of a blade holder drive gear and a counterweight which is utilized to counterbalance the effect of the reciprocable blade holder and blade assembly. This object is accomplished by partially receiving the drive gear in a recess that is formed in the counterweight.
In further accordance with this invention the counterweight is provided with a novel simplified, three-point guide arrangement for guiding the reciprocable motion of the counterweight. According to the preferred embodiment of this invention, this guide arrangement comprises a guide pin which received with a sliding fit in a slot at the upper end of the counterweight and a pair of guide bearing members which receive the oppositely facing side edges of the counterweight.
According to this invention the sabre saw housing is longitudinally split, and the above-mentioned guide pin is traped in position between the complementary halves of the split housing. The above-mentioned counterweight guide bearing members are separably snapped into position in cavities which are formed in the complementary housing halves.
Accordingly, another important object of this invention is to provide a novel guide structure for a counterweight in a sabre saw, and still another object of this invention is to provide a novel support for the above-mentioned counterweight guide structure in the sabre saw housing.
Prior to this invention various configurations have been proposed for mounting a sabre saw shoe platen or base of the housing of the sabre saw. One example, involving a nontiltable base is described in U.S. Pat. No. 3,186,454 issued to S. H. Kohler et al on June 1, 1965.
In comparison with the foregoing construction, this invention provides for a tiltable base assembly which is so constructed and arranged as to be supported from a split housing solely by separable seating engagement with interior surfaces on the halves of the housing. According to this aspect of the present invention, the base assembly comprises a longitudinally extending rod member which pivotally supports the shoe platen and which is trapped between the complementary halves of the split housing.
Thus, another object of this invention is to provide a novel sabre saw having a tiltable base assembly wherein a part of the base assembly is trapped between complementary halves of a longitudinally split housing.
Still another object of this invention is to provide a novel sabre saw having a gear and blade holder compartment which is formed in the tool housing and which is partitioned from the remaining interior of the housing so that a lubricating grease introduced into the compartment does not escape into other parts of the housing containing an electric motor and switch assembly which supplies operating power for the saw blade.
Still another object of this invention is to provide a power driven tool with a novel bearing holder assembly.
According to the preferred embodiment of this invention, the bearing holder comprises an insert member and a cover or cap for supporting an inboard armature shaft bearing in the tool housing. The insert member is fixed in the housing, and the cover is detachably secured to the insert member. The insert member has a locating boss which transversely positions the cover. The outer periphery of the inboard bearing has a spherical contour which cooperates with a mating seat on the cover to position the cover axially of the bearing holder axis. The cover is also formed with a bore for mounting a gear-supporting idler shaft. Thus the axis of the idler shaft is fixed in parallel relation to the revolution axis of the seat on the cover, and the locating boss positions the cover so that the revolution axis of the seat on the cover is coincident with the axis of revolution of the bearing seat on the insert member.
Further objects of this invention will appear as the description proceeds in connection with the below-described drawings and the appended claims.